getroot.c

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/* getroot.c: get the root dentry for an NFS mount
 *
 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/init.h>

#include <linux/time.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/stats.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/lockd/bind.h>
#include <linux/seq_file.h>
#include <linux/mount.h>
#include <linux/vfs.h>
#include <linux/namei.h>
#include <linux/security.h>

#include <asm/uaccess.h>

#include "internal.h"

#define NFSDBG_FACILITY     NFSDBG_CLIENT

/*
 * Set the superblock root dentry.
 * Note that this function frees the inode in case of error.
 */
static int nfs_superblock_set_dummy_root(struct super_block *sb, struct inode *inode)
{
    /* The mntroot acts as the dummy root dentry for this superblock */
    if (sb->s_root == NULL) {
        sb->s_root = d_make_root(inode);
        if (sb->s_root == NULL)
            return -ENOMEM;
        ihold(inode);
        /*
         * Ensure that this dentry is invisible to d_find_alias().
         * Otherwise, it may be spliced into the tree by
         * d_materialise_unique if a parent directory from the same
         * filesystem gets mounted at a later time.
         * This again causes shrink_dcache_for_umount_subtree() to
         * Oops, since the test for IS_ROOT() will fail.
         */
        spin_lock(&sb->s_root->d_inode->i_lock);
        spin_lock(&sb->s_root->d_lock);
        hlist_del_init(&sb->s_root->d_alias);
        spin_unlock(&sb->s_root->d_lock);
        spin_unlock(&sb->s_root->d_inode->i_lock);
    }
    return 0;
}

/*
 * get an NFS2/NFS3 root dentry from the root filehandle
 */
struct dentry *nfs_get_root(struct super_block *sb, struct nfs_fh *mntfh,
                const char *devname)
{
    struct nfs_server *server = NFS_SB(sb);
    struct nfs_fsinfo fsinfo;
    struct dentry *ret;
    struct inode *inode;
    void *name = kstrdup(devname, GFP_KERNEL);
    int error;

    if (!name)
        return ERR_PTR(-ENOMEM);

    /* get the actual root for this mount */
    fsinfo.fattr = nfs_alloc_fattr();
    if (fsinfo.fattr == NULL) {
        kfree(name);
        return ERR_PTR(-ENOMEM);
    }

    error = server->nfs_client->rpc_ops->getroot(server, mntfh, &fsinfo);
    if (error < 0) {
        dprintk("nfs_get_root: getattr error = %d\n", -error);
        ret = ERR_PTR(error);
        goto out;
    }

    inode = nfs_fhget(sb, mntfh, fsinfo.fattr);
    if (IS_ERR(inode)) {
        dprintk("nfs_get_root: get root inode failed\n");
        ret = ERR_CAST(inode);
        goto out;
    }

    error = nfs_superblock_set_dummy_root(sb, inode);
    if (error != 0) {
        ret = ERR_PTR(error);
        goto out;
    }

    /* root dentries normally start off anonymous and get spliced in later
     * if the dentry tree reaches them; however if the dentry already
     * exists, we'll pick it up at this point and use it as the root
     */
    ret = d_obtain_alias(inode);
    if (IS_ERR(ret)) {
        dprintk("nfs_get_root: get root dentry failed\n");
        goto out;
    }

    security_d_instantiate(ret, inode);
    spin_lock(&ret->d_lock);
    if (IS_ROOT(ret) && !(ret->d_flags & DCACHE_NFSFS_RENAMED)) {
        ret->d_fsdata = name;
        name = NULL;
    }
    spin_unlock(&ret->d_lock);
out:
    if (name)
        kfree(name);
    nfs_free_fattr(fsinfo.fattr);
    return ret;
}